A portable telephone system, such as the second-generation digital cordless telephony (CT2), has multiple transceivers which are located at a call point station or base station known as a telepoint. This telepoint base station can be public and accessible by anyone fulfilling its requirements or the base station can be private, such as one in a private residence, home, office, hostel or other locations where there is a limited number of users. These transceivers allow persons using portable or wireless telephones or handsets to access a link on a communication resource, such as an available radio frequency (RF) channel. In accordance with a call set-up process, the channel is allocated by one of the transceivers to the public service telephone network (PSTN) after an initial registration process has been completed.
In the private environment, registration is the process where the user manually keys up a non-registered base station to initiate registration and commands the handset to register itself to the non-registered base station. According to the Common Air Interface (CAI) standard that the CT2 system follows, and for double protection, each base station has a unique identification number "base ID" and the portable telephone or handset also has a unique identification "handset ID." During this registration process both the handset and the base station exchange identification such that each will have each other's identification stored in its memory. Hence, the "handset ID" is stored in the base station and the "base ID" is stored in the portable telephone. In other words, both identification numbers are stored in both locations.
After the handset has successfully registered itself to the now registered base station, it can then use the registered base station to make (or receive) phone calls in tile call set-up process. Before allowing a user of the handset to place a call from the registered base station, the user has to select and use a particular base identification (base ID) as the link ID (LID) in a link request, during the CT2 call set-up process. Conventionally, to establish this link from the handset to one of the base station's transceivers to remotely connect with the PSTN, the portable telephone uses the "base ID" as the LID to request for a link. The base station, upon recognizing its own "base ID", would grant a link to the portable telephone. Hence, the user has to manually select the correct "base ID" to link up to the right base. If the user has roamed from one base station to another, this LID entering process can be quite tiresome especially since the "base ID" is a four digit hexadecimal number.
The following is an example of the current CT2 call set-up process:
Under the following given conditions: PA1 Registration slot 1 : 5678 PA1 Registration slot 2 : 9876 PA1 Portable telephone 1234 PA1 Base ID 4321 PA1 Registration slot 1: 5678 PA1 Registration slot 2: 9876 PA1 Registration slot 3: 4321
Portable telephone ID=1234 PA2 Base station 1 base ID=5678 PA2 Base station 2 base ID=9876 PA2 Base station 3 base ID=4321
Assuming the portable telephone already has registered with base stations 1 and 2, stored in the portable telephone's memory is thus the following information:
The portable telephone is now registering to base station 3. Before registration, base station 3 does not have the identification for portable telephone 1234. After registration, Base station 3 has the following information stored in its memory:
And the portable telephone has the following information stored in its memory:
Assuming the portable telephone display is currently showing the contents of memory registration slot 1, which is the base ID 5678, because the user had just previously gone back to base station 1 to make a call. Assuming also, the user has now moved to base station 3 to make another call and thus is requesting a link with base station 3. If the user does not change the handset's current memory registration display slot, still showing 5678, when base station 3 receives the link request from portable telephone 1234, base station 3 will not recognize the LID of 5678 as a valid base ID request, even though base station 3 recognizes the portable telephone as one of it's registered telephone. Therefore, the link request is not accepted and a link grant is not transmitted. Only when the user changes the handset's current memory registration display slot to show 4321, will base station 3 recognize the LID as a valid base ID request in order to transmit a link grant to the handset 1234.
Accordingly, there is a need to make the call set-up process more user friendly by allowing a handset to place a call from a registered base station without having to select and use a particular base identification as the link ID during the link request in a CT2 communication system.